1. Technical Field
This invention relates in general to computer hard disk drives and in particular to an apparatus and method for reducing and/or preventing mechanical shock-induced damage between an actuator arm and a disk file in a computer hard disk drive.
2. Description of the Related Art
Generally, a digital data storage system consists of one or more storage devices that store data on storage media such as magnetic or optical data storage disks. In magnetic disk storage systems, a storage device is called a hard disk drive (HDD), which includes one or more disks and an HDD controller to manage local operations concerning the disks. Hard disks are platters, typically made of aluminum alloy, plastic substrates, or a mixture of glass and ceramic, covered with a magnetic coating. Typically, two or three platters are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
The only other moving part within a typical HDD is the head assembly. Within most drives, one read/write head is associated with each side of each platter and flies just above or in contact with the platter's surface. Each read/write head is connected to a semi-rigid arm apparatus which supports the entire head flying unit. More than one of such arms may be utilized together to form a single armature unit.
Each read/write head scans the hard disk platter surface during a "read" or "write" operation. The head/arm assembly is moved utilizing an actuator which is often a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which is mounted a spindle supporting the disks. The base casting is in turn mounted to a frame via a compliant suspension. When current is fed to the motor, the VCM develops force or torque which is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head nears the desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
If a hard disk drive sustains severe vibration or mechanical shock during operation, the arms of the actuator can contact the disks and may damage them. Although some hard disk drives have restraint mechanisms for withstanding high G-force impacts, they are typically limited to a single non-operational application. For example, a common prior art solution employs a stationary ramp located adjacent to the radial outer edge of the disk pack. When the heads on the arms of the actuator are rotated beyond the outer edges of the disks, the heads or arms are parked on the ramp and are unable to contact the disks. Unfortunately, this design is capable of protecting the drive only when the heads are radially outside of the disks.
In U.S. Pat. No. 5,668,682, a detachable disk drive having a head lift mechanism is disclosed. The mechanism moves the actuator arm and, thus, the head away from the disk when the drive is removed from a slot in a laptop computer. When the drive is inserted into the slot in the laptop computer, the actuator arm is automatically released so that the head may contact the disk for normal read/write operations. Unfortunately, the mechanism is limited to preventing contact between the actuator arm and the disk when the drive is removed from the laptop computer. Thus, if the laptop undergoes shock when the drive is installed, the actuator arm will not be prevented from striking the disk, regardless of the operational status of the drive of the radial position of the actuator arm. Therefore, an improved disk drive for preventing shock-induced contact between the actuator arm and disk is needed.